The present invention is in the field of plasma torches and in particular is directed to a plasma torch having an improved pilot and main arc generating circuit.
Plasma torches, otherwise known as electric arc torches, are known in the art for performing operations, such as cutting, welding, etc , on workpieces, and operate by directing a plasma consisting of ionized gas particles towards a workpiece. An example of the conventional single gas plasma torch is illustrated in Hatch, U.S. Pat. No. 3,813,510, assigned to the assignee herein Other patents disclosing such torches are U.S. Pat. Nos. 4,225,769; 4,663,512; and 4,663,515. The disclosures of all of the above-mentioned patents are incorporated herein by reference thereto. As these patents illustrate, a gas to be ionized, such as nitrogen, is fed through channels in the torch mechanism in such a manner as to swirl in front of the end of a negatively charged electrode. The welding tip which is adjacent the end of the electrode has a sufficiently high voltage applied thereto to cause a spark gap to jump between the electrode and the welding tip, thereby heating the gas and causing it to ionize. A pilot DC voltage between the electrode and the welding tip maintains the pilot arc. The iononized gas in the gap appears as a flame and extends externally of the tip where it can be seen by the operator. The extension of the pilot arc and the flame, which for practical purposes, may be considered as being co-extensive depends upon the power in the gapxe2x80x94i.e., the arc currentxe2x80x94as well as the pressure of the gas forced into the gap and out of the torch. The pilot arc provides a source of light which enables the operator to see the proper position for the torch before starting the welding or cutting operation. In actual practice, when the pilot arc is on, a loop-shaped arc extending out of the torch can be seen. As the torch head is brought down towards the workpiece, the pilot arc jumps from the electrode to the workpiece due to the fact that the impedance of the workpiece current path is lower than the impedance of the welding tip current path.
Conventional single gas plasma torches include pilot arc circuits which provide a 20-40 amp. pilot arc current at 100-200 volts across the electrode-tip gap, resulting in an extension of the arc about xc2xc-xc2xd inch past the welding tip. As a consequence, the torch must be brought to within about xc2xc-xc2xd inch of the workpiece before the transfer arc jumps to the workpiece. This creates difficulties in the starting of cutting or welding operations.
It is an object of the invention to provide a plasma arc torch circuit which is more efficient than prior art circuits and which regulate the power source in response to sensing of the torch arch  arc transferring from between the pilot electrode and the torch electrode, to torch electrode and the work member. 
It is another object of the invention to optimize the power regulator design with respect to semiconductor switch and diode stresses, transformer and inductor design and overall component count.
It is still a further object to provide a plasma arc torch with smoother on-plate transfer dynamics
Briefly stated, the present invention comprises new electronic circuit concepts for a plasma arc torch wherein main current regulated power means regulates the pilot current prior to main arch transfer Further, the circuit may contain two inductors to which DC current initially flows but is interrupted upon main arc transfer such that one inductor maintains the pilot arc while the current in the second inductor forces the establishment of the transferred arc. Also, advantages are presented in pulsing the cutting arc as well as pulsing the pilot arc.
These, as well as other objects and advantages will become more apparent upon a reading of a detailed description of the preferred embodiment in conjunction with the drawings, wherein: